Preheat the oven to 250 degrees F. Set a wire rack on a rimmed baking sheet. Peel and rinse the potatoes, then grate on the large holes of a box grater into a colander set over a large bowl. Grate the onion into the colander; season with 1 teaspoon salt and 1/2 teaspoon pepper. Squeeze the potato mixture with your hands to remove as much liquid as possible, transferring the mixture to a paper towel-lined plate as you go. Wipe out the bowl. Blot the potato mixture dry with paper towels and return to the dry bowl.
Peel the beet and grate on the large holes of the box grater; add to the bowl with the potato mixture. Add the egg, matzo meal and parsley and stir to combine. Scoop tablespoonfuls of the potato mixture and tightly pack into 1-inch pancakes (about 24); transfer to a large plate.
Heat 1/4 inch schmaltz or vegetable oil in a large nonstick skillet over medium heat. Working in batches, add the pancakes and fry until browned and crisp, 3 to 4 minutes per side. Transfer to the prepared baking sheet; sprinkle with salt and keep warm in the oven (or serve at room temperature). Top as desired.